The invention disclosed herein pertains to a tester for testing mass airflow (MAF) sensors that are commonly used on motor vehicles having a computer controlled engine performance system.
The MAF sensor is usually mounted in the vehicle between the air cleaner and the throttle plate assembly. The MAF sensor generates electric pulses at a rate or frequency proportional to the volume of the atmospheric air entering the engine intake manifold. In some designs, the MAF sensor also incorporates a temperature sensor to measure the temperature of the air entering the engine. A thermistor is usually used to sense the air temperature and may be positioned and associated with the MAF sensor or it may be located elsewhere on the vehicle.
A typical MAF sensor heats an element such as a wire or a foil that is disposed in the stream of air flowing into the engine. The temperature of the sensing element is controlled by the computer so that the element is always at a specific number of degrees warmer than incoming atmospheric air. The electric power required to maintain this elevated temperature is measured and translated into mass airflow by the computer. The computer uses the mass airflow value to calculate the amount of fuel required to maintain the desired air/fuel ratio to the engine. The MAF sensor assembly contains a voltage-to frequency converter that generates the square wave electric pulse train. Typical pulse rates or frequencies are about 30 Hz at idle speed and 150 Hz at wide open throttle.